目录:
一、什么是AutoLayout?
二、创建autoLayout的方法
三、VFL语言
 
 
一、什么是AutoLayout?
  Autolayout是一种“自动布局”技术,专门用来布局UI界面的,Autolayout自iOS6开始引入,由于Xcode 4的不给力,当时并没有得到很大推广。自iOS 7(Xcode 5)开始,Autolayout的开发效率得到很大的提升,Autolayout能很轻松地解决屏幕适配的问题。苹果官方也推荐开发者尽量使用Autolayout来布局UI界面。

  1、Autolayout的2个核心概念

  (1)参照:将某个UI控件作为参照标示,进行确定该控件的位置;

  (2)约束:为控件的布局进行加入限定,实现无论在ipad、iPhone设备上都能按照限定的格式、位置进行显示。
  2、添加约束的规则

  在添加时要注意目标view需要遵循以下规则:

  1)对于两个同层级view之间的约束关系,添加到它们的父view上

iOS_AutoLayout自动布局-LMLPHP

  2)对于两个不同层级view之间的约束关系,添加到他们最近的共同父view上

iOS_AutoLayout自动布局-LMLPHP

  3)对于有层次关系的两个view之间的约束关系,添加到层次较高的父view上

 iOS_AutoLayout自动布局-LMLPHP

 二、创建autoLayout的方法

  1、手动布局

iOS_AutoLayout自动布局-LMLPHP

  2、纯代码方式

  2.1代码实现Autolayout的步骤

  (1)利用NSLayoutConstraint类创建具体的约束对象

  (2)添加约束对象到相应的view上

  - (void)addConstraint:(NSLayoutConstraint *)constraint;
  - (void)addConstraints:(NSArray *)constraints;
  案例代码:
#import "ViewController.h"

@interface ViewController ()
@property(strong,nonatomic)UIView *view1;
@property(strong,nonatomic)UIView *view2;
@end @implementation ViewController - (void)viewDidLoad {
[super viewDidLoad];
//创建view1
self.view1 = [[UIView alloc]init];
self.view1.backgroundColor = [UIColor redColor];
self.view1.translatesAutoresizingMaskIntoConstraints = NO;
[self.view addSubview:self.view1]; //创建view2
self.view2 = [[UIView alloc]init];
self.view2.backgroundColor = [UIColor yellowColor];
self.view2.translatesAutoresizingMaskIntoConstraints = NO;
[self.view addSubview:self.view2]; //创建约束
//设置view1的左边距
NSLayoutConstraint *lcLeft = [NSLayoutConstraint constraintWithItem:self.view1 attribute:NSLayoutAttributeLeading relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeLeading multiplier:1.0 constant:];
//设置view1的下边距
NSLayoutConstraint *lcBottom = [NSLayoutConstraint constraintWithItem:self.view1 attribute:NSLayoutAttributeBottom relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeBottom multiplier:1.0 constant:-];
//设置view1与view2等宽
NSLayoutConstraint *lcEqualWidth = [NSLayoutConstraint constraintWithItem:self.view1 attribute:NSLayoutAttributeWidth relatedBy:NSLayoutRelationEqual toItem:self.view2 attribute:NSLayoutAttributeWidth multiplier:1.0 constant:];
//设置view1与view2等高
NSLayoutConstraint *lcEqualHeight = [NSLayoutConstraint constraintWithItem:self.view2 attribute:NSLayoutAttributeHeight relatedBy:NSLayoutRelationEqual toItem:self.view1 attribute:NSLayoutAttributeHeight multiplier:1.0 constant:];
//设置view2的右边距
NSLayoutConstraint *lcRight = [NSLayoutConstraint constraintWithItem:self.view2 attribute:NSLayoutAttributeTrailing relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeTrailing multiplier:1.0 constant:-];
//设置view2的下边距
NSLayoutConstraint *lcBottom2 = [NSLayoutConstraint constraintWithItem:self.view2 attribute:NSLayoutAttributeBottom relatedBy:NSLayoutRelationEqual toItem:self.view attribute:NSLayoutAttributeBottom multiplier:1.0 constant:-];
//设置view1与view2的间隔
NSLayoutConstraint *lcGap = [NSLayoutConstraint constraintWithItem:self.view2 attribute:NSLayoutAttributeLeading relatedBy:NSLayoutRelationEqual toItem:self.view1 attribute:NSLayoutAttributeTrailing multiplier:1.0 constant:];
//添加约束到组
[self.view addConstraints:@[lcLeft,lcBottom,lcRight,lcBottom2,lcEqualHeight,lcEqualWidth,lcGap]];
//设置view的高度
NSLayoutConstraint *lcFixedHeight = [NSLayoutConstraint constraintWithItem:self.view1 attribute:NSLayoutAttributeHeight relatedBy:NSLayoutRelationEqual toItem:nil attribute:NSLayoutAttributeHeight multiplier:1.0 constant:];
[self.view1 addConstraint:lcFixedHeight];
}
@end

  运行效果图,如下所示:

iOS_AutoLayout自动布局-LMLPHP

  2.2代码实现Autolayout需要注意以下三点:

  (1)要先禁止autoresizing功能,设置view的下面属性为NO

  view.translatesAutoresizingMaskIntoConstraints = NO;

  (2)添加约束之前,一定要保证相关控件都已经在各自的父控件上

  (3)不用再给view设置frame

  2.3创建约束对象的常用方法

  +(id)constraintWithItem:(id)view1 attribute:(NSLayoutAttribute)attr1 relatedBy:(NSLayoutRelation)relation toItem:(id)view2 attribute:(NSLayoutAttribute)attr2 multiplier:(CGFloat)multiplier constant:(CGFloat)c;

  参数解析:

  (1)view1 :要约束的控件

  (2)attr1 :约束的类型(做怎样的约束)

  (3)relation :与参照控件之间的关系

  (4)view2 :参照的控件

  (5)attr2 :约束的类型(做怎样的约束)

  (6)multiplier :乘数

  (7)c :常量

三、VFL语言

  VFL全称是Visual Format Language,翻译过来是“可视化格式语言”,VFL是苹果公司为了简化Autolayout的编码而推出的抽象语言。

  1、简单VFL示例:

  1.[button]-[textField]

  iOS_AutoLayout自动布局-LMLPHP

  2.[button(>=50)]

iOS_AutoLayout自动布局-LMLPHP

  3.|-50-[purpleBox]-50-|

  iOS_AutoLayout自动布局-LMLPHP

  4.V:[topField]-10-[bottomField]

iOS_AutoLayout自动布局-LMLPHP

  5.[maroonView][blueView]

iOS_AutoLayout自动布局-LMLPHP

  6.[button(100@20)]

iOS_AutoLayout自动布局-LMLPHP

  7.[button(==button2)]

iOS_AutoLayout自动布局-LMLPHP

  8.[flexibleButton(>=70,<=100)]

  iOS_AutoLayout自动布局-LMLPHP

  9.|-[find]-[findNext]-[findField(>=20)]-|

iOS_AutoLayout自动布局-LMLPHP

  2.复杂示例(带说明):

  H:[cancelButton(72)]-12-[acceptButton(50)]

  说明:canelButton宽72,acceptButton宽50,它们之间间距12  

  H:[wideView(>=60@700)]

  说明:wideView宽度大于等于60point,该约束条件优先级为700(优先级最大值为1000,优先级越高的约束越先被满足)

  V:[redBox]-[yellowBox(==redBox)]

  说明:竖直方向上,先有一个redBox,其下方紧接一个高度等于redBox高度的yellowBox

  H:|-10-[Find]-[FindNext]-[FindField(>=20)]-|

  说明:水平方向上,Find距离父view左边缘默认间隔宽度,之后是FindNext距离Find间隔默认宽度;再之后是宽度不小于20的FindField,它和FindNext以及父view右边缘的间距都是默认宽度。(竖线“|”表示superview的边缘)

  3.使用VFL来创建约束数组

  + (NSArray *)constraintsWithVisualFormat:(NSString *)format options:(NSLayoutFormatOptions)opts metrics:(NSDictionary *)metrics views:(NSDictionary *)views;

  参数说明:

  (1)format :VFL语句

  (2)opts :约束类型

  (3)metrics :VFL语句中用到的具体数值

  (4)views :VFL语句中用到的控件

  案例分析:通过VFL语句实现上个案例

#import "ViewController.h"

@interface ViewController ()
@property(strong,nonatomic)UIView *view1;
@property(strong,nonatomic)UIView *view2; @end @implementation ViewController - (void)viewDidLoad {
[super viewDidLoad];
//创建view1
self.view1 = [[UIView alloc]init];
self.view1.backgroundColor = [UIColor redColor];
self.view1.translatesAutoresizingMaskIntoConstraints = NO;
[self.view addSubview:self.view1];
//创建view2
self.view2 = [[UIView alloc]init];
self.view2.backgroundColor = [UIColor blueColor];
self.view2.translatesAutoresizingMaskIntoConstraints = NO;
[self.view addSubview:self.view2]; //使用VFL语言添加约束
NSDictionary *metrics = @{@"gap":@,@"height":@};
NSDictionary *viewsDic =@{@"view1":self.view1,@"view2":self.view2};
NSArray *layoutConstraints1 = [NSLayoutConstraint constraintsWithVisualFormat:@"H:|-gap-[view1]-gap-[view2(==view1)]-gap-|" options:NSLayoutFormatDirectionLeftToRight metrics:metrics views:viewsDic];
NSArray *layoutConstraints2 = [NSLayoutConstraint constraintsWithVisualFormat:@"V:[view1(height)]-gap-|" options:NSLayoutFormatDirectionLeadingToTrailing metrics:metrics views:viewsDic];
NSArray *layoutConstraints3 = [NSLayoutConstraint constraintsWithVisualFormat:@"V:[view2(==view1)]-gap-|" options:NSLayoutFormatDirectionLeadingToTrailing metrics:metrics views:viewsDic];
[self.view addConstraints:layoutConstraints1];
[self.view addConstraints:layoutConstraints2];
[self.view addConstraints:layoutConstraints3]; } @end
05-11 22:13